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162 Theodor and Foss sister-group to a monophyletic Artiodactyla + Cetacea (Cetartiodactyla) (Thewissen et al., 2001); and one in which mesonychids are the sister-taxon to a paraphyletic Artiodactyla. In the latter topology, Cetacea is nested within the Artiodactyla as the sister-taxon to the extant hippopotamids (Geisler and Uhen, 2003). The new fossils have refuted a sister-taxon relationship between whales and mesonychids, and affirmed a strong relationship between whales and artiodactyls, but have not provided strong support for a whale–hippo relationship. This is not surprising, given that early whales and all artiodactyls share the character of the double-trochleated astragalus, and the new specimens do not seem to provide character evidence uniquely linking whales and hippos to the exclusion of other artiodactyls. Morphological suites of characters that support the placement of whales within Artiodactyla have been difficult to find because the phylogenetic relationships within early Artiodactyla are poorly resolved (Gentry and Hooker, 1988; Scott and Janis, 1993; Stucky, 1998; Geisler, 2001b) and relevant taxa are poorly represented in many phylogenetic studies. Aside from Luckett and Hong’s (1998) work on the 6-cusped dp4, little attention has been paid to other characters of the deciduous teeth in phylogeny reconstructions. Deciduous dentitions from several genera belonging to the Eocene European artiodactyl family Cebochoeridae have second and third deciduous premolars (dp2–3) that possess accessory denticles and resemble the deciduous and adult teeth of derived archaeocete whales. These teeth do not resemble the adult cebochoerid premolars or any other artiodactyl dentition (adult or juvenile) we examined. This similarity between cebochoerid artiodactyls and archaeocete whales has not previously been noted; presumably because deciduous teeth are seldom preserved, and the resemblances are obscured by wear in most fossilized deciduous teeth. Among the specimens examined, one particular specimen of Cebochoerus lautricensis, from the Aquitanian Basin, France, MNHN.EBA 327 (Fig. 1), has relatively unworn juvenile teeth and displays the unusual morphology also found in more heavily worn specimens of cebochoerid subadults (Fig. 2(c–f)). The discovery of this specimen led us to review the deciduous dentition of cebochoerids in more detail, and to test whether the similarities in the juvenile lower premolars of cebochoerids to archaeocete teeth represented a synapomorphy or convergence. MATERIALS AND METHODS We describe below the deciduous dentitions of the cebochoerid genera Cebochoerus and Acotherulum, based on the following specimens: Acotherulum sp.: MNHN.Qu7075, right maxilla with dP2-4, M1-2 (Fig. 3(b)); Qu7076, right dentary with dp3-m2 (Fig. 3(c and d)); Qu98, anterior mandible with fused symphysis, alveoli for dp1-2, dp3-m1 present; Qu88, right dentary with alveoli for part of dp2 and dp3, dp4-m3 present, m3 partially erupted; Qu89 ?Acotherulum left dentary with alveoli for dp1-2, dp3-m1 present. Acotherulum saturninum: MNHN.LDB106, right dentary with dp3-m1 (m1 broken); LDB107, right maxilla with dP2-M1. Cebochoerus sp.: MNHN.Qu53 right dentary with broken p1, dp2-m3, m3 partially erupted (Fig. 3(f)). Cebochoerus minor: MNHN.Qu11283, left maxilla fragment with dP3-M1 (Fig. 3(a)); Qu11284, left maxilla fragment with dP3-M1; Qu65, right dentary fragment with dp3-m1 (Fig. 3(e)); Qu66, right dentary fragment with broken dp4-m2; Qu61, left dentary fragment with broken dp4-m3, m3 partially erupted. Cebochoerus lautricensis: MNHN.EBA327, left dentary with dp2-m2 (Fig. 1).
Cebochoerid Deciduous Dentitions 163 Fig. 1. Deciduous teeth of Cebochoerus lautricensis, MNHN.EBA327. a. buccal view dp2-m2, b. lingual view of dp2-3, c. buccal view of dp2-3. Scale bars denote 1 cm. No juvenile specimens of the genus Gervachoerus are known (Erfurt, personal communication). Juvenile dentitions of Diacodexis (UMMP 79924, 79083, 86533, 82909); Antiacodon (CMNH 53969), and other artiodactyls, along with the archaeocete Dorudon (NHM M10174), (Uhen, 2004) were examined for comparison. We performed a phylogenetic analysis of artiodactyls, whales, and mesonychids, using a data matrix drawn from characters in the literature (Blainville, 1816; Webb and Taylor, 1980; Cifelli, 1982; Pickford, 1983; Novacek, 1986; Shoshani, 1986; Gentry and Hooker, 1988; Thewissen and Domning, 1992; Thewissen et al., 1994, 2001; Gingerich et al., 1995; O’Leary and Rose, 1995; Zhou et al., 1995; Theodor, 1996; Geisler and Luo, 1998; Luckett and Hong, 1998; O’Leary, 1998; O’Leary and Geisler, 1999; Thewissen and Madar, 1999; Geisler, 2001a) and including new data from the deciduous dentition. Taxa were chosen to include representatives from most of the basal lineages of artiodactyls, because any rigorous test of the whale–hippo hypothesis must include these lineages to polarize the characters and place the hippos and whales within a complete phylogenetic context. The following taxa are used in this analysis (taxa with genera in parentheses are composites coded based on all of the genera listed): Arctocyon, Hyopsodus, Phenacodus, and Meniscotherium are included as outgroups; the archaic ungulate Eoconodon; the mesonychians Sinonyx, Dissacus, Pachyaena, Harpagolestes, Synoplotherium, Mesonyx, and Hapalodectes; the cetaceans Artiocetus, Ambulocetus, Pakicetus, Georgiacetus, Basilosaurus, and Dorudon; and the artiodactyls Diacodexis pakistanensis, Diacodexis secans, Bunomeryx, Antiacodon, Homacodon, leptochoerid (Stibarus and
Page 1: Journal of Mammalian Evolution, Vol
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